Medical procedures involving access to the brain through a burr hole in the skull are under increasing use. Such procedures may include electrical stimulation of the brain for purposes such as relief of chronic pain and treatment of movement disorders, and the use of parenchymal or intracerebroventricular catheters for infusing pharmaceutical agents. A typical electrical brain stimulation system includes a pulse generator operatively connected to the brain by a lead having at its distal end an electrode designed to be implanted within the brain, and having at its proximal end a connector assembly designed to connect to the pulse generator. Use of a parenchymal catheter generally involves the insertion of a catheter within the brain to dispense pharmaceutical agents at a specific desired location.
One aspect of the above-listed procedures, and of any other such procedures that involve instrument access to the brain through a burr hole, is the precision with which any such inserted devices, e.g., catheters and leads, are placed. Once a satisfactory burr hole is established at a particular site, to avoid unintended injury to the brain, physicians typically use stereotactic procedures to position the inserted devices. One stereotactic instrument which may be used, for example, to position a lead electrode is disclosed in U.S. Pat. No. 4,350,159 to Gouda. As can be appreciated, once an inserted device is properly positioned, it is important that the device not be moved. Even one millimeter of travel of the positioned device may cause unsatisfactory results or, in some cases, potential injury to the brain. Accordingly, reliable methods and apparatus for fixing the positioned device at the burr hole are beneficial.
Previous systems for securing a positioned device within a burr hole have had drawbacks. For instance, U.S. Pat. No. 4,328,813 to Ray discloses a socket and cap arrangement in which the cap is positioned so as to trap a positioned electrical stimulation lead between the socket and cap. That arrangement involved securing the lead off-center from the burr hole in a manner such that, during installation of the anchoring cap, a stereotactic instrument could not be used to support the lead. Often the lead was manually supported in place while the anchoring cap was being installed. The lead was thus potentially susceptible to inadvertent movement by the physician during cap installation. Further, the interaction of the cap and socket could pull on the lead and potentially result in movement or dislodgement of the same.